Pause TransformFeedback before eglMakeCurrent. On Android Adreno eglMakeCurrent resets TransformFeedback position. Workaround is to pause TransformFeedback before eglMakeCurrent and resume afterwards. BUG=angleproject:1426 TEST=TransformFeedbackTest.MultiContext Change-Id: I4fdb9edbd28b4b16c01d1a94419e78160b31b79f Reviewed-on: https://chromium-review.googlesource.com/355676 Reviewed-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Geoff Lang <geofflang@chromium.org> Commit-Queue: Yuly Novikov <ynovikov@chromium.org>